The primary foci of this study are to explore specific mechanisms that regulate biosynthetic enzyme synthesis, and to uncover common points of regulation shared by amino acid biosynthetic pathway enzymes and the cognate aminoacyl-transfer ribonucleic acid synthetases. The principal approach we are using is to select analog-resistant mutants and screen for altered regulatory properties. Studies in this laboratory are focused on biosynthesis of the branched-chain amino acids. Our concentration is upon regulation of acetohydroxy acid synthetase formation and the roles that transfer ribonucleic acids (tRNA) and aminoacyl-tRNA synthetases play in controlling the biosynthesis of isoleucine, valine, and leucine. We are studying multiple-genetic-site involvement in AHAS biosynthesis and mapping mutations which appear to result in common point control alteration. These studies are being conducted primarily in Escherichia coli K-12 and Salmonella typhimurium LT-2.